RFR: CODETOOLS-7903400: DEFAULT_UNIX_ENV_VARS needs to be updated

Thu Apr 27 19:28:22 UTC 2023

Please review a small change to add additional environment variables that may be required on some Unix-like platforms.

The additions include:
* `DBUS_SESSION_BUS_ADDRESS`
* `WAYLAND_DISPLAY`
* all `XDG_*` variables

There is some related additional cleanup in this area as well.

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Commit messages:
 - CODETOOLS-7903400: DEFAULT_UNIX_ENV_VARS needs to be updated
 - CODETOOLS-7903400: DEFAULT_UNIX_ENV_VARS needs to be updated

Changes: https://git.openjdk.org/jtreg/pull/152/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=152&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903400
  Stats: 30 lines in 2 files changed: 19 ins; 6 del; 5 mod
  Patch: https://git.openjdk.org/jtreg/pull/152.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/152/head:pull/152

PR: https://git.openjdk.org/jtreg/pull/152